1. Field of the Invention
The present invention relates to a transmission output control device and radio equipment including the same, and more specifically, a transmission output control device to control the transmission signal to be emitted from an antenna, and a radio equipment including the same.
2. Description of the Related Art
Generally, in radio equipment such as some cellular phone terminals, the transmission output level of the transmission signal at the terminal is switched in multiple stages or continuously, in response to instructions from a base station, to reduce power consumption or to reduce interference with other terminals.
FIG. 10 is a block diagram illustrating a basic constitution of a transmission part of the cellular phone terminal with circuits for controlling the transmission output as described above. A transmission output control device 50 is provided with a directional coupler 51 and a detector 52.
A carrier-wave signal generated in an oscillator 53 is converted into the transmission signal through various processing circuits including an amplifier 54, and inputted to a high output amplifier 55. The transmission signal amplified by this high output amplifier 55 is inputted to an antenna multicoupler 56 through the directional coupler 51, and transmitted by an antenna 57 after unwanted signals are removed by the antenna multicoupler 56. Further, a reception signal received by the antenna 57 is inputted to a reception part Rx after unwanted signals are removed by the antenna multicoupler 56. The instruction information for controlling the transmission output level of the transmission signal is included in the above-described reception signal from the base station.
The directional coupler 51 comprises a main line 51-1 and a sub line 51-2, whereby part of the transmission signal from the high output amplifier 55 is branched, that is, taken out from one end of the sub line 51-2 and inputted to the detector 52. A terminating resistor R51 is connected to the other end of the sub line 51-2. In the detector 52, the transmission signal is rectified by a detection diode D51, smoothed by a smoothing capacitor C51 and then, changed into a detection signal by a load resistor R52. The detection signal is inputted to a control circuit 58 as the TSSI (Transmitting Signal Strength Indicator) signal corresponding to the transmission output level of the transmission signal actually being transmitted from the antenna 57.
A control part 59 provides a control signal to the control circuit 58 to indicate a target transmission output level, in response to an instruction from a base station not indicated in the figure. The control circuit 58 generates a feedback (FB) signal in response to the control signal from the control part 59, having such a value as to reduce the difference between the actual transmission output level as indicated by the TSSI signal and the target transmission output level. The FB signal is outputted to a control terminal Tc which is capable of controlling the high output amplifier 55 in order to set the actual transmission output level.
As described above, a transmission output control system a part of which comprises the transmission output control device 50 forms a feedback loop, and controls the transmission output level so that the actual transmission output level is changed to the target transmission output level as specified by the control part 59.
Recently in North America, a dual-band type cellular phone terminal which is usable in both the AMPS (Advanced Mobile Phone Services: 800 MHZ) band and the PCS (Personal Communication Services: 1900 MHZ) band has been developed.
FIG. 11 is a block diagram illustrating a basic constitution of a transmission part of the above-described dual-band type cellular phone terminal. A transmission output control device 60 is provided with first and second directional couplers 61a, 61b and a detector 62. The transmission output control device 60 constitutes the transmission output control system forming the feedback loop together with first and second high output amplifiers 63a, 63b, a control circuit 64 and a control part 65. The operation of the transmission output control system including the transmission output control device 60 is the same as that of the transmission output control system including the transmission output control device 50 of FIG. 10.
The conventional transmission output control devices described above are formed by respectively mounting discrete parts constituting a directional coupler, a detector and a tuner on a circuit substrate. As a result, the transmission output control device and the entire radio equipment are increased in size.
Further, because the discrete parts constituting the directional coupler, the detector and the tuner of the transmission output control device are connected to each other by wiring provided on the circuit substrate, losses due to the wiring are increased, and there has been a problem that the characteristic of the transmission output control device is degraded.
In addition, in the dual-band equipment, a gap between the two directional couplers must be ensured to obtain isolation between them, and thus, the transmission output control device and the entire radio equipment are further increased in size.
To overcome the above described problems, embodiments of the present invention provide a compact transmission output control device with excellent characteristics and radio equipment including the same.
One embodiment of the present invention provides a transmission output control device comprising: a directional coupler which branches a part of a transmission signal amplified by a high output amplifier; and a detector which detects a part of said branched transmission signal; wherein said directional coupler and said detector are integrated in a laminated body comprising a plurality of dielectric layers.
According to the above described structure and arrangement, all the wiring of the directional coupler and the detector can be provided inside the laminated body because the directional coupler and the detector which constitute the transmission output control device are integrated within the laminated body. Thus, the loss in each portion of the wiring can be reduced, so that the transmission output control device with excellent characteristic can be obtained.
In the above described transmission output control device, the directional coupler may include a main line and a sub line; the detector may include a detection diode, a smoothing capacitor and a load resistor; the detection diode and the load resistor of the detector may be mounted on the outside of the laminated body; the main line and the sub line of the directional coupler may comprise strip line electrodes provided inside the laminated body; and the smoothing capacitor of the detector may comprise a capacitor electrode and a ground electrode arranged opposite each other on opposite sides of one or more of said dielectric layers inside said laminated body.
According to the above described structure and arrangement, the number of parts of the transmission output control device can be reduced because the main line and the sub line of the directional coupler comprise strip line electrodes provided inside the laminated body, and the smoothing capacitor of the detector comprises the capacitor electrode and the ground electrode provided inside the laminated body. Thus, a compact transmission output control device can be obtained, and the area occupied by the transmission output control device can be reduced in radio equipment in which this transmission output control device is mounted.
In the above described transmission output control device, a plurality of directional couplers may be provided; and the plurality of said directional couplers may be usable for controlling transmission signals of different frequencies and disposed on different ones of the plurality of dielectric layers. Thus, sufficient isolation between a plurality of directional couplers can be ensured. As a result, a transmission output control device with excellent characteristics can be obtained.
Another embodiment of the present invention provides radio equipment including the above described transmission output control device. According to the above described structure and arrangement, the radio equipment can be made compact while keeping excellent transmission characteristic because a compact transmission output control device with excellent characteristic is used.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.